This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Streptolysin S (SLS) is a potent cytolysin produced by Streptococcus Pyogenes. SLS plays a key role in virulence and is responsible for the b-hemolytic phenotype of these bacteria. To date, the structure of SLS has not been identified. Previous studies have shown that SLS is a heavily posttranslationally modified ribosomally encoded peptide. In order for the peptide to become cytolytic the side chains of one or more of the cysteine, serine or threonines are heterocyclized into five membered thiazole or oxazole rings. Repeated attempts to identify and map these posttranslational modifications by mass spectrometry have failed. This study will use NMR to do a sequential assignment by triple resonance on a recombinantly produced SLS analogue.